Lombok学习笔记

August 27, 2023 1 minute read

Lombok是我们在工作中常用的工具，写一篇文章整理一下用法。

使用Maven导入lombok

        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <version>1.18.28</version>
            <scope>provided</scope>
        </dependency>

具体用法

`val`

相当于final var

`var`

用于声明局部变量

public class Main {
    public static void main(String[] args) {
        var name = "123";
        final var age = 1;
        System.out.println(age);
        System.out.println(name);
    }
}

`@NonNull`

用于方法的参数空指针校验。当为null时默认抛出throw new NullPointerException("param is marked non-null but is null");

public class Main {
    public static void main(String[] args) {
        test(null);
    }

    static void test(@NonNull People people) {
        System.out.println(people.getName());
    }
}

`@Cleanup`

用于一个资源自动释放。默认在方法执行的最后执行close()释放资源，对于没有该方法的对象，可在@Cleanup()中指定相应的无参方法。释放资源方法需要参数的，不可用该注解。

public class Main {
    public static void main(String[] args) throws IOException {
        @Cleanup InputStream in = new FileInputStream("src/main/java/org/example/Main.java");
        @Cleanup OutputStream out = new FileOutputStream("src/main/java/org/example/test.java");
        byte[] b = new byte[10000];
        in.read(b);
        out.write(b);
    }
}

public class Main {
    public static void main(String[] args) throws IOException {
        @Cleanup("dispose") org.eclipse.swt.widgets.CoolBar bar = new CoolBar(parent, 0);
    }
}

注意：cleanup方法只在资源不为null的时候执行。如果代码抛出异常，且清理方法也抛出异常，原始的异常会被cleanup隐藏。这种情况不建议使用该注解。

`@Getter and @Setter`

生成成员变量的get和set方法，且默认都为public，可使用AccessLevel指定。

public class People {
    @Getter
    @Setter
    private String name;
    
    @Getter
    @Setter(AccessLevel.PRIVATE)
    private Boolean isFoo;
}

也可以在类上使用，相当于对所有的非静态成员变量使用。

@Getter
@Setter
public class People {
    private String name;

    private Boolean isFoo;
}

`@ToString`

让lombok实现toString()

@ToString()
public class People {
    @Setter
    private String name;

    @Setter
    @ToString.Exclude
    private Boolean isFoo;
}

People(name=123)

`@EqualsAndHashCode`

生成equals和hashcode方法

@EqualsAndHashCode
public class People {
    private String name;

    @EqualsAndHashCode.Exclude
    private Boolean isFoo;
}

`@NoArgsConstructor, @RequiredArgsConstructor and @AllArgsConstructor`

@NoArgsConstructor:生成非空构造函数

@RequiredArgsConstructor: 为所有@NonNull生成构造函数

@AllArgsConstructor:生成全部参数的构造函数

@AllArgsConstructor
@NoArgsConstructor
@RequiredArgsConstructor
public class People {
    private String name;

    private Boolean isFoo;

    @NonNull
    private Integer age;

    @NonNull
    private String address;
}

`@Data`

相当于@ToString+@EqualsAndHashCode+@Getter+@Setter+@RequiredArgsConstructor

`@Value`

所有的filed都是private final

相当于final @ToString @EqualsAndHashCode @AllArgsConstructor @FieldDefaults(makeFinal = true, level = AccessLevel.PRIVATE) @Getter

`@Builder`

建造者模式

@Builder
public class PeopleBuilder {
    private String name;

    private Boolean isFoo;

    private Integer age;

    private String address;
}

public class Main {
    public static void main(String[] args) throws IOException {
        PeopleBuilder.builder().isFoo(true).build();
    }
}

`@SneakyThrows`

偷偷抛出受检查的异常，无需用throws写，需要谨慎使用

public class Main implements Runnable {
    @SneakyThrows(FileNotFoundException.class)
    public static void main(String[] args) {
        FileInputStream fileInputStream = new FileInputStream("ss");
    }

    @SneakyThrows
    @Override
    public void run() {
        throw new Throwable();
    }
}

`@Synchronized`

用于静态或者实例方法。类似synchronized

`@With`

生成除关联对象之外的克隆。用于对象final变量的修改。

@AllArgsConstructor
@ToString
public class People {
    private final String name;

    @With
    private final Integer age;
}

public class Main {
    public static void main(String[] args) {
        People people = new People("11", 2);
        System.out.println(people.withAge(4));
        System.out.println(people);
    }
}

People(name=11, age=4)
People(name=11, age=2)

`@Getter(lazy=true)`

将某一个计算需要耗费大量CPU或者内存的变量缓存起来

public class GetterLazyExample {
    @Getter(lazy=true) private final double[] cached = expensive();

    private double[] expensive() {
        double[] result = new double[1000000];
        for (int i = 0; i < result.length; i++) {
            result[i] = Math.asin(i);
        }
        return result;
    }
}

`@Log`

生成日志变量

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